In general, the present invention relates to CMOS circuitry and, more particularly, to switched capacitor amplifiers.
Analog integrated circuits (ICs) are integrated circuits that process analog signals. Examples of such circuits may include, for example, amplifiers, reference current sources, and reference voltage sources. Digital integrated circuits are ICs which process digital signals. Examples of digital integrated circuits may include, for example, logical circuit and state machines, such as processors.
Some integrated circuits, however, may process both analog and digital signals. Such circuits are known as mixed signal integrated circuits. Mixed signal ICs may require the use of a DC bias current supply. A common example of a mixed signal circuit is an analog-to-digital converter (ADC). ADCs, such as pipelined ADCs, may accept an input analog signal and produce an output digital signal having a value corresponding to the magnitude of the input analog signal. ADCs may be found in numerous products, such as CMOS based imaging products. CMOS imaging products may include ICs that include a plurality of ADCs, so that a plurality of analog signals may be simultaneously converted to corresponding digital signals.
Most CMOS imagers have a maximum power consumption value, which they may not exceed. The ADCs' constant consumption of current from the DC bias current supply forms a significant part of the maximum power consumption value for most imagers. Accordingly, it is desirable to reduce imager power consumption attributable to sources other than consumption of the DC bias current.
One such source of power consumption by the ADCs themselves is the switched capacitor amplifiers that make up the various stages of pipelined ADCs. Switched capacitor amplifiers may include a number of switches. Charge injection from turning on or off at least some of the switches contributes to a relatively long settling time of the switched capacitor amplifier, which increases ADC power consumption.